fix grok pattern typo

Author: fbaligand

snippets/logstash-filters.json

@@ -178,7 +178,7 @@
     "prefix": "lf-grok",
     "body": [
       "grok {",
-      "\tmatch => { \"${field}\" => \"${pattern\"}",
+      "\tmatch => { \"${field}\" => \"${pattern}\"}",
       "}"
     ],
     "description": "Logstash grok Filter"
@@ -413,4 +413,4 @@
     ],
     "description": "Logstash zeromq Filter"
   }
-}
+}